libsyscall/wrappers/mach_absolute_time.s

   1 /*
   2  * Copyright (c) 2003-2007 Apple Inc. All rights reserved.
   3  *
   4  * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License. The rights granted to you under the License
  10  * may not be used to create, or enable the creation or redistribution of,
  11  * unlawful or unlicensed copies of an Apple operating system, or to
  12  * circumvent, violate, or enable the circumvention or violation of, any
  13  * terms of an Apple operating system software license agreement.
  14  *
  15  * Please obtain a copy of the License at
  16  * http://www.opensource.apple.com/apsl/ and read it before using this file.
  17  *
  18  * The Original Code and all software distributed under the License are
  19  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  20  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  21  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  22  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  23  * Please see the License for the specific language governing rights and
  24  * limitations under the License.
  25  *
  26  * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
  27  */
  28
  29 #include <sys/appleapiopts.h>
  30 #include <machine/cpu_capabilities.h>
  31
  32 #if defined(__i386__)
  33
  34 /* return mach_absolute_time in %edx:%eax
  35  *
  36  * The algorithm we use is:
  37  *
  38  *      ns = ((((rdtsc - rnt_tsc_base)<<rnt_shift)*rnt_tsc_scale) / 2**32) + rnt_ns_base;
  39  *
  40  * rnt_shift, a constant computed during initialization, is the smallest value for which:
  41  *
  42  *  (tscFreq << rnt_shift) > SLOW_TSC_THRESHOLD
  43  *
  44  * Where SLOW_TSC_THRESHOLD is about 10e9.  Since most processor's tscFreq is greater
  45  * than 1GHz, rnt_shift is usually 0.  rnt_tsc_scale is also a 32-bit constant:
  46  *
  47  *      rnt_tsc_scale = (10e9 * 2**32) / (tscFreq << rnt_shift);
  48  */
  49
  50         .globl _mach_absolute_time
  51 _mach_absolute_time:
  52         pushl   %ebp
  53         movl    %esp,%ebp
  54         pushl   %esi
  55         pushl   %ebx
  56
  57 0:
  58         movl    _COMM_PAGE_NT_GENERATION,%esi   /* get generation (0 if being changed) */
  59         testl   %esi,%esi                       /* if being updated, loop until stable */
  60         jz      0b
  61
  62         lfence
  63         rdtsc                                   /* get TSC in %edx:%eax */
  64         lfence
  65
  66         subl    _COMM_PAGE_NT_TSC_BASE,%eax
  67         sbbl    _COMM_PAGE_NT_TSC_BASE+4,%edx
  68
  69     /*
  70      * Prior to supporting "slow" processors, xnu always set _NT_SHIFT to 32.
  71      * Now it defaults to 0, unless the processor is slow.  The shifts
  72      * below implicitly mask the count down to 5 bits, handling either default.
  73      */
  74         movl    _COMM_PAGE_NT_SHIFT,%ecx
  75         shldl   %cl,%eax,%edx                   /* shift %edx left, filling in from %eax */
  76         shll    %cl,%eax                        /* finish shifting %edx:%eax left by _COMM_PAGE_NT_SHIFT bits */
  77
  78         movl    _COMM_PAGE_NT_SCALE,%ecx
  79
  80         movl    %edx,%ebx
  81         mull    %ecx
  82         movl    %ebx,%eax
  83         movl    %edx,%ebx
  84         mull    %ecx
  85         addl    %ebx,%eax
  86         adcl    $0,%edx
  87
  88         addl    _COMM_PAGE_NT_NS_BASE,%eax
  89         adcl    _COMM_PAGE_NT_NS_BASE+4,%edx
  90
  91         cmpl    _COMM_PAGE_NT_GENERATION,%esi   /* have the parameters changed? */
  92         jne     0b                              /* yes, loop until stable */
  93
  94         popl    %ebx
  95         popl    %esi
  96         popl    %ebp
  97         ret
  98
  99 #elif defined(__x86_64__)
 100
 101 /*
 102  * 64-bit version _mach_absolute_time.  We return the 64-bit nanotime in %rax.
 103  *
 104  * The algorithm we use is:
 105  *
 106  *      ns = ((((rdtsc - rnt_tsc_base)<<rnt_shift)*rnt_tsc_scale) / 2**32) + rnt_ns_base;
 107  *
 108  * rnt_shift, a constant computed during initialization, is the smallest value for which:
 109  *
 110  *      tscFreq << rnt_shift) > SLOW_TSC_THRESHOLD
 111  *
 112  * Where SLOW_TSC_THRESHOLD is about 10e9.  Since most processor's tscFreqs are greater
 113  * than 1GHz, rnt_shift is usually 0.  rnt_tsc_scale is also a 32-bit constant:
 114  *
 115  *      rnt_tsc_scale = (10e9 * 2**32) / (tscFreq << rnt_shift);
 116  *
 117  */
 118         .globl  _mach_absolute_time
 119 _mach_absolute_time:
 120         pushq   %rbp                            // set up a frame for backtraces
 121         movq    %rsp,%rbp
 122         movq    $(_COMM_PAGE_TIME_DATA_START),%rsi
 123 1:
 124         movl    _NT_GENERATION(%rsi),%r8d       // get generation
 125         testl   %r8d,%r8d                       // if 0, data is being changed...
 126         jz      1b                              // ...so loop until stable
 127         lfence
 128         rdtsc                                   // edx:eax := tsc
 129         lfence
 130         shlq    $32,%rdx                        // rax := ((edx << 32) | eax), ie 64-bit tsc
 131         orq     %rdx,%rax
 132
 133     /*
 134      * Prior to supporting "slow" processors, xnu always set _NT_SHIFT to 32.
 135      * Now it defaults to 0, unless the processor is slow.  In order to maintain
 136      * compatibility with both old and new versions of xnu, we mask the shift
 137      * down to 0x1F, which maps the old default (32) into the new default (0).
 138      */
 139         movl    _NT_SHIFT(%rsi),%ecx
 140         andl    $0x1F,%ecx                      // *** remove this line once 10.9 is GM ***
 141         subq    _NT_TSC_BASE(%rsi), %rax        // rax := (tsc - base_tsc)
 142         shlq    %cl,%rax                        // rax := (tsc - base_tsc) << NT_SHIFT
 143         movl    _NT_SCALE(%rsi),%ecx
 144         mulq    %rcx                            // rdx:rax := ((tsc - base_tsc)<<shift) * scale
 145         shrdq   $32,%rdx,%rax                   // divide by 2**32
 146         addq    _NT_NS_BASE(%rsi),%rax          // (((tsc - base_tsc) * scale) >> 32) + ns_base
 147
 148         cmpl    _NT_GENERATION(%rsi),%r8d       // did the data change during computation?
 149         jne     1b
 150         popq    %rbp
 151         ret
 152
 153 #else
 154 #error Unsupported architecture
 155 #endif